I tried this exercise at the gym called hyperextension. At first, I was not aware of the name of the exercise. Until Ravi Singh told me, that is. All I knew was people lean their bellies on waist-high surface and start doing sit-up-like movements.

Like this.

I thought it would train the muscles on my stomach and started doing it, two days in a row at the gym.

... I knew better today after waking up to the most awful pain my hamstrings ever experienced. =__=